This invention relates to apparatus for rapidly cooling a sensor into the cryogenic temperature range, and, more particularly, to a dewar structure that supports the sensor and promotes the rapid cooling.
Many types of devices, such as infrared detectors, are operated at very low temperatures, as for example 77K or less. In some cases, low temperature operation is required because physical or chemical processes of interest occur only at low temperature, and in other cases because some types of electrical-thermal noise are reduced at low temperature. An approach to cool the device to low temperature is therefore required.
The simplest and most direct approach to cooling a device to a low operating temperature is to place the device into a bath of a liquefied gas whose normal boiling temperature is approximately the desired operating temperature. This approach is preferred in many laboratory situations, but it is not practical for the cooling of sensors in mobile applications such as missiles, or inaccessible applications such as spacecraft, where it is not possible to store liquid coolants for extended periods of time.
Rapid cooldown times without use of liquefied gases are achieved with a Joule-Thomson gas expansion cryostat. The cryostat expands a pressurized gas to form a coolant stream which may contain cold gas, liquefied gas, or both. The coolant stream absorbs heat from the surroundings and carries it away, leaving a cooled structure.
Some specialized devices and cooling systems have unique packaging and space limitations. For example, an infrared heat seeking detector in the nose of a missile must be securely supported and rapidly cooled upon demand, but the overall size and weight of the cooling system is severely limited by the overall system constraints.
Thus, while Joule-Thomson cryostat cooling offers the greatest promise for rapid cooldown of sensors and their related structure, the constraints imposed by missile sensor applications require continuing improvement in both the cryostat and the sensor packaging. There are requirements for ever-shorter cooldown times of the sensors to an operational state from an uncooled state, and there is an ongoing need for cooling techniques that achieve such reduced cooldown times while meeting space and weight requirements. The present invention fulfills this need, and further provides invention fulfills this need, and further provides related advantages.